1) Hydrocarbons sind chemicals which are build only of hydrogen and carbon. Petrochemicals ar e chemicals which are usually derived from petroleum or natural gas. They are build of hydrogen, carbon, but also other chemical elements for instance oxygen. 2) "Petrochemicals can be defined as any of a large group of chemicals (as distinct from fuels) derived from petroleum and natural gas and used for a variety of commercial purposes. The definition, however, has been broadened to include the whole range of aliphatic, aromatic, and naphthenic organic chemicals, as well as carbon black and such inorganic materials as sulfur and ammonia. Petrochemical feedstocks can be classified into three general groups: olefins, aromatics and a third group that includes synthesis gas and inorganics. In many instances, a specific chemical included among the petrochemicals may also be obtained from other sources, such as coal, coke, or vegetable products. For example, materials such as benzene and naphthalene can be made from either petroleum or coal, while ethyl alcohol may be of petrochemical or vegetable origin." "Hydrocarbon - an organic compound (as acetylene or butane) containing only carbon and hydrogen and often occurring in petroleum, natural gas, coal, and bitumens." Source and further information: http://www.npradc.org/news/facts/petrochemical.cfm Further information: http://en.wikipedia.org/wiki/Petrochemical http://en.wikipedia.org/wiki/Hydrocarbon